LAMBDA UMI (Lambda Ursae Minoris). Our focus in the northern
hemisphere is ultimately on Polaris, the
North Star, the luminary of Ursa Minor,
which closely marks the North Celestial
Pole, the point of the sky's apparent rotation. Though other
stars surround the pole, they are so overwhelmed by Polaris's fame
and brilliance that they go rather unnoticed (the problem added to
by the occasional difficulty of using telescopes near the pole).
They are also a rather strange bunch. So begins a continuing tale
of "polar stars," those within a few
degrees of the pole. If you define the limit to naked-eye vision
as 6.5 (at the bottom of generic "sixth magnitude" and admittedly on
the faint side), then Lambda Ursae Minoris (about halfway between
Yildun and Polaris) just
makes it over the mark at faint sixth (6.38), which

Polaris is centered in a six-degree-wide field of view that shows
a variety of "polar stars." Lamdba Ursae Minoris is the reddish
star up and to the right of Polaris. Roughly between them lies the
North Celestial Pole, around which they all seem to revolve.
Yildun (Delta UMi) is the
brighter of the pair at the upper right corner.

See the full-resolution image and more on
polar stars in the
Polar Project.

gives it some distinction as the closest naked-eye star to the Pole
other than Polaris itself. (Number 3 in both brightness and
position is HR 286, which is
only a third of a degree from Polaris, and at magnitude of 6.47
just barely makes it as well.) Lambda is just under a degree from
the true pole, which lies more or less between it and Polaris
(which is slightly closer). As a result of the Earth's axial precession (the 26,000-year axial
wobble), a couple hundred years ago, Lambda was in fact the better
pole star. The pole will actually pass between Lambda and Polaris
about the year 2060. While the Greek
letter name looks "Bayerish," it is not, as the star does not
appear on Bayer's Uranometria, nor was it
so named by the late 1700s, but was applied later. Physically it
is a relatively rare class M (M1) giant 880 or so light years away.
Seriously neglected, over the past 20 years it has been mentioned
in a mere dozen research papers, and in none has it been the focus.
There is no measured temperature, the spectral class giving 3800
Kelvin. With that to account for infrared radiation, Lambda UMi
shines with the luminosity of 600 Suns,
and is a swollen red giant
with a radius 57 times solar, about 69 percent the size of
Mercury's orbit. With a mass somewhere around 1 1/2 to 2 solar
masses, it is either still brightening with a dead helium core or
has begun to fuse helium and is fading some as it readjusts itself.
Though Lambda is rated as double, the companion is a 14th
magnitude star a hefty 55 seconds of arc away. Typical of the
"polar stars," it has not been observed for a century, so it is not
possible to tell whether it is a real companion or not. If it is,
it has the luminosity of a class K dwarf, is at least 15,000
Astronomical Units away from Lambda proper, and orbits with a
period greater than a million years. From there, the giant would
appear as a brilliant reddish dot shining the light of our full
Moon.